An electrochemical battery stores electrical energy by an electrochemical reaction termed charging, and then later delivers the stored electrical energy by reversal of the reaction, termed discharging. An event of discharging constitutes one-half of a cycle and an event of charging constitutes one half of the cycle, so that a single battery cycle includes consecutive events of discharging and charging. The battery is typically formed of a number of individual electrochemical cells. Each electrochemical cell has characteristic voltage and current properties. The electrical cells are electrically interconnected to provide the desired voltage and current characteristics required for the battery.
A typical lithium ion battery cell includes a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, and an electrolyte that saturates the separator and provides a lithium ion path between the negative electrode and the positive electrode. The negative electrode typically has a negative current collector contacting the negative electrode active material, and a positive current collector contacting the positive electrode active material. The negative electrode active material releases lithium ions upon discharging of the battery cell and absorbs lithium ions upon charging of the battery cell. The positive electrode active material reacts with lithium ions upon discharging of the battery cell and releases lithium ions upon charging of the battery cell. A lithium ion battery incorporates at least two, and typically a large number, of these cells within a container. These cells are wired in series to achieve the desired voltage.
Each current collector provides an electrical current flow path between its respective electrode active material and a terminal, and thence to an external circuit. The current collector is a metal that is resistant to corrosion in the electrolyte, typically copper for the negative current collector and aluminum for the positive current collector. There must be good mechanical adhesion between each of the current collectors and its respective active material. A low electrical resistance at the interface between the current collector and the active material is also important, because the interface is in series with the current flow and imposes an interface impedance on the current flow.
Lithium ion batteries experience a steady loss in capacity when operated in a continuous cyclic regime. Since lithium batteries are expensive to replace, and in some applications, such as satellite applications, virtually impossible to replace, what is needed is a means to restore the capacity of lithium ion batteries without replacing the batteries.